1. Field
The following description relates to aggregated graphene oxide and a preparing method thereof, aggregated graphene and a preparing method thereof, and aggregated and nitrogen-doped graphene and a preparing method thereof.
2. Description of Related Art
Graphene is generally a carbon structure of a two-dimensional nano-sheet monolayer, in which sp2 carbon atoms form a hexagonal honeycomb lattice. Graphene was first discovered by the Novoselov's and Geim's research team in Britain in 2004 from graphite through mechanical exfoliation [Novoselov K et al., Electric field effect in atomically thin carbon films, Science, 306:666, 2004]. It is a material, which has been spotlighted as a groundbreaking new material by virtue of its significantly high specific surface area (theoretical value of 2,600 m2/g), superior electronic conduction property, and physical (typical value of 8×105 S/cm from the view point of quantum mechanics) and chemical stability. Further, graphene has limitless applicability in energy storage materials (lithium ion secondary cells, hydrogen storage fuel cells, and super capacitors) for various devices upon nano-complexation with a transition metal, gas sensors, micro-components for medical engineering, high functional composites, and so on.
However, graphene is not easily exfoliated in a solution due to the van der Waals operation between graphene layers resulting from the bond of sp2 carbons on a surface of the graphene. Accordingly, Graphene is mostly present as thick multilayer graphene rather than single layer graphene. Even if graphene is exfoliated, it tends to be restacked. Accordingly, there is a problem in that where a composite material is synthesized with transition metal oxide in a solution by using graphene as a precursor, it is difficult to utilize the high specific surface area of the monolayer graphene and form a uniformed composite structure. This problem impedes the utility of the transition metal oxide.
In order to overcome the problem, there has been suggested an activity treatment method using potassium hydroxide or carbon dioxide. For example, it was reported that while graphene, which has been subject to heat treatment through the activity treatment process using potassium hydroxide, exhibits a high specific surface area (3,100 m2/g), the activity treatment affects the typical 2D structure of the graphene [Carbon-Based Supercapacitors Produced by Activation of Graphene, Yanwu Zhu et al., Science 332, 1537 (2011)]. Activity treatment using carbon dioxide is suitable for graphite, but graphene oxide is highly likely to be explored and completely oxidized during the activity treatment process.